Micro-droplet generation method based on three-section type air pressure waveform

Abstract

The invention relates to the technical field of microfluid precision control, and discloses a micro-droplet generation method based on a three-section type air pressure waveform, which comprises the following steps: a microcontroller sends a time sequence instruction to drive a pneumatic assembly to act, and stages of constant high-pressure pushing, rapid pressure relief and oscillation negative pressure pullback are sequentially executed in a fluid pipeline; in the pushing stage, the stable-pressure gas is used for driving liquid to extend to form a liquid column; in the pressure relief stage, the micro valve is reset to be matched with the front-end one-way pressure relief valve to quickly discharge residual high pressure; in the pull-back stage, a Helmholtz oscillation system formed by a main gas circuit pipeline and a valve port is used for inducing aerodynamic resonance, and reverse negative pressure waves are generated and directly act on the root of a liquid column to promote physical fracture of the liquid column. Through the synergistic effect of an active excitation negative pressure pull-back mechanism and a front-end rapid pressure relief strategy, trailing caused by fluid viscosity is effectively overcome, satellite liquid drops are eliminated, the problem of pressure lag is solved, and high-precision lossless generation of picoliter-to-nanoliter micro-droplets is achieved.

Description

Technical Field

[0001] This invention relates to the field of microfluidic precision control technology, specifically to a method for generating microdroplets based on a three-segment gas pressure waveform. Background Technology

[0002] In modern precision manufacturing and analysis fields such as in vitro diagnostics, high-throughput drug screening, microelectronic packaging, and bioprinting, extremely high precision is required for the dispensing of microfluidics, typically necessitating the precise transfer of liquids at the picoliter or nanoliter level onto the target substrate. Among various fluid dispensing technologies, pneumatic microdroplet generation technology is widely used due to its simple structure, controllable cost, and good compatibility with fluids of varying viscosities. Traditional pneumatic dispensing systems usually employ a time- and pressure-controlled mode, determining the amount of liquid dispensed by controlling the duration of solenoid valve opening and the amplitude of air source pressure.

[0003] However, with the increasing demand for miniaturization and high precision, traditional pneumatic technology faces physical limitations. Due to the compressibility of air, when a pneumatic controller is connected to the nozzle via a long conduit, a capacitor-like energy storage circuit forms inside the conduit. At the end of the dispensing cycle, after the solenoid valve closes and cuts off the air supply, the high-pressure gas accumulated in the conduit cannot dissipate instantly. This hysteresis effect in pressure transmission causes a slow pressure drop at the nozzle. This delayed pressure decay not only limits the minimum droplet size, making it difficult for the system to stably output picolinate or nanoliter droplets, but also causes liquid slack, affecting the consistency and repeatability of dispensing.

[0004] Furthermore, in the dynamics of droplet separation, the surface tension and viscosity of the fluid itself are the main factors hindering droplet detachment from the nozzle. Under conventional square wave pneumatic drive mode, droplets mainly rely on inertial force or gravity to overcome surface tension and achieve separation. For fluids with small volume or high viscosity, due to the lack of an active breakup mechanism, the liquid is prone to excessive stretching when detaching from the nozzle, forming a thin liquid bridge. When the liquid bridge eventually breaks, the residual liquid often agglomerates again into tiny, unintended satellite droplets, splashing around the target point, causing sample contamination or circuit short circuits. Although there are existing technologies that use constant negative pressure for back suction to try to balance pipeline pressure or prevent dripping, this passive static negative pressure is difficult to precisely match with the high-speed dynamic jetting process: too low a negative pressure cannot effectively break the droplets, while too high a negative pressure can easily draw air into the nozzle and disrupt the fluid state, making it difficult to apply precise braking or shearing action to the root of the liquid column on a millisecond timescale, and failing to meet the requirements for droplet morphology integrity and landing accuracy in high-precision scenarios. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a microdroplet generation method based on a three-segment pneumatic waveform, which solves the problems of droplet tailing, satellite droplet generation, and difficulty in achieving precise separation of picoliter-level micro-fluids caused by slow release of residual pressure in pipelines and fluid viscosity in existing pneumatic micro-dispensing technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a microdroplet generation method based on a three-segment air pressure waveform. This method is applied to a microdroplet generation system. By using a microcontroller to perform time-sequential control of pneumatic components, a specific air pressure evolution process is constructed in the fluid pipeline to achieve precise injection and separation of micro-fluids.

[0008] The method of the present invention mainly includes driving the pneumatic components to move by sending timing control commands from a microcontroller, and sequentially executing a constant high pressure pushing stage, a rapid pressure relief stage, and an oscillating negative pressure pull-back stage in the fluid pipeline.

[0009] During the constant high-pressure driving phase, the microcontroller sends an opening signal to the high-speed three-way solenoid microvalve. This signal drives the valve core to switch positions, connecting the positive pressure input and output. At this time, the constant high-pressure gas, buffered by the pressure stabilizing chamber, is transmitted to the front end along the main gas pipeline. The pressure stabilizing chamber, acting as a gas buffer container, rapidly increases the pressure in the fluid pipeline to a preset positive pressure peak at the moment the opening signal is triggered, and maintains a constant pressure amplitude throughout the pulse width duration. This constant high-pressure drive causes the liquid meniscus within the nozzle module to overcome surface tension and extend at the nozzle orifice, forming a liquid column.

[0010] During the rapid depressurization phase, the system operates according to a preset timing logic. When the duration of the activation signal reaches the preset pulse width, the microcontroller cuts off the activation signal. The high-speed three-way solenoid microvalve then resets, cutting off the positive pressure input and connecting the output terminal to the waveform shaping terminal. At this time, the high-pressure gas accumulated in the pipeline has two release paths: part of it enters the negative pressure generating component through the waveform shaping terminal, and the other part is released to the external environment through the one-way pressure relief valve located on the Helmholtz oscillation module.

[0011] During the oscillating negative pressure pull-back phase, resonance is induced using the acoustic structural characteristics of the gas path system. The main gas path pipe in the system is configured as an oscillating cavity with a large volume, while the waveform shaping end of the high-speed three-way solenoid microvalve and the exhaust port of the front-end one-way pressure relief valve constitute the oscillating neck that communicates with the outside. When the high-pressure gas is rapidly released through the aforementioned neck during the pressure relief phase, the inertial effect of the gas mass interacts with the volumetric elastic effect of the pipeline cavity, inducing underdamped aerodynamic resonance inside the fluid pipeline. This aerodynamic resonance induces a reverse negative pressure wave in the fluid pipeline. Since the high-speed three-way solenoid microvalve is in a state where the output end and the waveform shaping end are connected at this time, this reverse negative pressure wave can pass through the valve body and propagate along the main gas path pipe to the front end, eventually reaching the nozzle. The negative pressure wave exerts a physical suction force on the root of the forming liquid column, causing the liquid column neck to break and separate rapidly, forming micro-droplets.

[0012] One of the key technologies involved in this invention is the dynamic response mechanism of the front-end one-way pressure relief valve. This one-way pressure relief valve is installed on the main gas pipeline and has a through-flow central channel and an elastic sealing element. During the constant high-pressure driving phase, high-speed airflow flows through the central channel. Utilizing fluid dynamics principles, the elastic sealing element overcomes the static pressure inside the pipe and adheres to the exhaust valve seat under the action of the airflow impact and adsorption force, sealing the exhaust path and ensuring lossless transmission of driving pressure. During the rapid pressure relief phase, as the driving source is cut off, the airflow velocity through the central channel decreases. The elastic sealing element, driven by the residual static pressure in the pipeline, disengages from the exhaust valve seat, opening the pressure relief path to the external environment, thus achieving rapid pressure release.

[0013] Furthermore, this microdroplet generation method also includes a liquid-filling mode. In liquid-filling mode, the rear-end pneumatic control module switches to a negative pressure suction state, forming a pressure gradient pointing towards the rear end inside the main air passage. At this time, the elastic sealing element of the one-way pressure relief valve generates a clamping force pointing towards the exhaust valve seat under the pressure difference between the external atmospheric pressure and the negative pressure inside the pipeline, thereby sealing the connection between the exhaust passage and the external environment. The nozzle module uses the negative pressure suction transmitted to the nozzle orifice to draw external liquid into the internal cavity of the nozzle body.

[0014] In terms of control strategy, the microcontroller sets a minimum critical threshold for pulse width, for example, 1.5 milliseconds. When the set pulse width is lower than this threshold, the microcontroller determines that the aerodynamic energy transmitted to the nozzle is insufficient to overcome the liquid surface tension barrier and prohibits the sending of the start signal to avoid ineffective injection.

[0015] Furthermore, this invention employs a dual-variable coordinated adjustment mechanism based on pressure amplitude and pulse width to control droplet volume. When generating tiny droplets close to the lower limit of the range, the system uses a combination of low pressure and short pulse width, and utilizes the reverse negative pressure wave generated during the oscillating negative pressure pull-back phase to directly act on the root of the liquid column, forcing it to break. When generating larger droplets close to the upper limit of the range, the system uses a combination of increasing the input pressure amplitude of the pressure stabilizing chamber and extending the pulse width to increase fluid acceleration and outflow time. This adjustment mechanism also includes compensation logic for different fluid viscosities. For fluids with viscosities ranging from 1 mPa·s to 1000 mPa·s, by increasing the input pressure and adjusting the pulse width, the volume of droplets ejected through the nozzle is maintained within a preset range, for example, between 400 picoliters and 20 nanoliters.

[0016] The method of the present invention also relates to configuring a nozzle module, wherein the nozzle has a single-hole micro-conical structure with a rear-end inner diameter larger than the front-end inner diameter. The method includes configuring a nozzle orifice diameter with predetermined flow resistance characteristics and setting a pulse width matching the nozzle orifice diameter to control the stability of the droplet's flight trajectory.

[0017] This invention provides a method for generating microdroplets based on a three-segment gas pressure waveform. It has the following beneficial effects:

[0018] 1. This invention constructs an integrated Helmholtz oscillation system, utilizing the main gas pipeline as a resonant cavity, and employing a micro-valve port and a one-way pressure relief valve as the oscillation neck. At the moment of rapid pressure relief, it actively induces pneumatic resonance. The reverse negative pressure wave generated by this resonance applies a physical pull-back force to the root of the liquid column at the critical moment of droplet formation, overcoming the fluid's viscosity and inertia, causing the liquid column to break sharply at the nozzle. This endogenous pull-back mechanism, requiring no additional oscillation elements, effectively solves the tailing and stringing problems commonly found in traditional pneumatic dispensing and prevents the formation of satellite droplets.

[0019] 2. This invention employs a one-way pressure relief valve with hydrodynamic response characteristics. Utilizing the impact-locking effect of high-speed airflow and the static pressure-driven opening effect, it achieves adaptive action without additional electrical control. During the pressure relief phase, the front-end one-way pressure relief valve not only quickly discharges residual high pressure in the pipeline nearby, eliminating pressure hysteresis, but also serves as the remote breathing port of the Helmholtz system, participating in the shaping of the gas pressure waveform and ensuring the steepness of the trailing edge of the drive pulse and the effectiveness of the pullback waveform. Simultaneously, in liquid suction mode, the valve utilizes differential pressure self-locking sealing, achieving bidirectional functional reuse of the gas path.

[0020] 3. This invention establishes a dual-variable collaborative adjustment mechanism based on the pressure amplitude of the pressure stabilizing chamber and the pulse width of the micro-valve. By increasing the input air pressure to compensate for the flow resistance loss of high-viscosity fluids, and in conjunction with millisecond-level precision pulse width modulation, the system can adapt to a variety of media from low to high viscosity. This adjustment method, combined with the flow resistance characteristics of the micro-conical nozzle, enables the system to cover droplet volume requirements across different orders of magnitude with a single hardware configuration. This avoids the need for frequent replacement of nozzle modules for different working conditions, thereby improving the versatility and operational efficiency of the equipment. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the microdroplet generation system based on a three-segment gas pressure waveform according to the present invention;

[0022] Figure 2 This is a flowchart illustrating the dynamic execution of the pneumatic circuit of the present invention.

[0023] Figure 3 This is a schematic diagram of the gas path state of the microdroplet generation system of the present invention in jet mode;

[0024] Figure 4 This is a schematic diagram of the gas path state of the microdroplet generation system of the present invention in liquid loading / liquid suction mode.

[0025] Among them, 110 is a microcontroller; 200 is a rear pneumatic control module; 210 is a high-speed three-way electromagnetic microvalve; 211 is the first port; 212 is the second port; 213 is the third port; 220 is a pressure stabilizing chamber; 230 is a negative pressure generator; 300 is a Helmholtz oscillation module; 310 is a one-way pressure relief valve; 400 is a nozzle module; 410 is a nozzle body; and 420 is a spray hole. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] See attached document Figure 1 This invention provides a microdroplet generation system based on a three-segment air pressure waveform. The system mainly includes a rear-end pneumatic control module 200, a Helmholtz oscillation module 300, and a nozzle module 400. The rear-end pneumatic control module 200 serves as the source of the air pressure waveform and is fluidly connected to the Helmholtz oscillation module 300 via an air passage. The Helmholtz oscillation module 300 is located at a handheld operating end, and its end is mechanically connected to and fluidly connected to the nozzle module 400.

[0028] In addition, the system includes a microcontroller 110, which is electrically connected to the back-end pneumatic control module 200 and the system power supply, respectively, and is used to send timing control commands to drive the movement of the pneumatic components. Specifically, a power drive circuit is also provided between the microcontroller 110 and the back-end pneumatic control module 200. The power drive circuit may include, for example, a MOSFET switching circuit or an H-bridge driver chip. The power drive circuit is configured to receive the low-power logic signal output by the microcontroller 110 and amplify it into a high-power electrical signal sufficient to drive the high-speed three-way solenoid microvalve 210.

[0029] The core component of the back-end pneumatic control module 200 is a high-speed three-way solenoid microvalve 210. The high-speed three-way solenoid microvalve 210 has three independent functional ports: a first port 211, a second port 212, and a third port 213. In this embodiment, the first port 211 is defined as the output terminal (A terminal), the second port 212 as the positive pressure input terminal (B terminal), and the third port 213 as the waveform shaping terminal (C terminal), which is connected to the negative pressure generator 230 or directly connected to the atmosphere. In this embodiment, the third port 213 serves as a key breathing neck of the Helmholtz oscillation system, matching the piping volume within the Helmholtz oscillation module 300. When the high-pressure gas is released via backflow, the flow resistance characteristics of the third port 213 participate in adjusting the resonant frequency within the gas path.

[0030] The Helmholtz oscillation module 300 not only performs the function of air pressure transmission but also constitutes the main body of the aerodynamic resonance. The main body of the Helmholtz oscillation module 300 is a main air passage pipe (i.e., oscillation chamber) with a predetermined volume. One end of the pipe is connected to the first port 211 of the high-speed three-way solenoid microvalve 210, and the other end is connected to the nozzle module 400. A one-way pressure relief valve 310 is also integrated into the Helmholtz oscillation module 300.

[0031] In this embodiment, the so-called Helmholtz oscillation cavity is not a single external component, but an integrated system concept composed of the following parts: a high-speed three-way solenoid microvalve 210 (serving as a narrow high-pressure airflow inlet and return neck), the main air path pipe in the Helmholtz oscillation module 300 (serving as a large-volume resonant cavity), and a one-way pressure relief valve 310 (serving as a distal variable breathing port). The acoustic characteristics of this system are determined by the length and diameter of the pipe and the equivalent cross-sectional area of ​​the valve port.

[0032] The one-way pressure relief valve 310 has a one-way flow structure, configured to allow gas to be rapidly discharged from the main gas pipeline to the external environment, while simultaneously blocking the entry of ambient air into the main gas pipeline. Depending on the actual manufacturing process, the specific structural form of the one-way pressure relief valve 310 can be selected from any one of a duckbill valve, an umbrella valve, or a spring-loaded ball valve. Preferably, in this embodiment, a duckbill valve structure made of soft rubber is used, utilizing the natural closing characteristics of its elastic lip to achieve sensitive sealing to small negative pressures and rapid opening under high-frequency positive pressure pulses.

[0033] The opening pressure threshold of the one-way pressure relief valve 310 is set to adapt to the working pressure of the system, so that the one-way pressure relief valve 310 can open to release residual positive pressure when the pipeline pressure drops due to the de-energization of the high-speed three-way solenoid microvalve 210. At the same time, the flow channel structure of the one-way pressure relief valve 310 is configured to allow negative pressure waves from the rear pneumatic control module 200 to pass through and be transmitted to the nozzle module 400.

[0034] The nozzle module 400 includes a nozzle body 410, the interior of which forms a cavity to accommodate the liquid to be sprayed. The end of the cavity extends to form a spray orifice 420. The spray orifice 420 has a single-hole micro-conical structure, its geometry characterized by a larger inner diameter at the rear end than at the front end, and the flow channel gradually converging to its minimum diameter along the liquid flow direction. The convergence angle of the spray orifice 420's cavity is set between 50 and 55 degrees.

[0035] The inner wall surface of the nozzle body 410 is coated with a superhydrophobic coating or polished to reduce liquid residue buildup. The internal geometry of the nozzle body 410 is configured such that the dead volume inside the nozzle is less than 20 nanoliters. The nozzle body 410 is made of a material selected from photosensitive resin, ceramic, metal, or ruby. In a specific embodiment using ruby, the dimensional tolerance of the nozzle orifice 420 is controlled within ±3 micrometers. The microcontroller 110 is configured to adjust the pulse width signal output to the high-speed three-way solenoid microvalve 210, with the pulse width adjustment range covering millisecond durations. Combined with air source pressure adjustment, this controls the droplet volume ejected through the nozzle orifice 420 to be between 400 picoliters and 20 nanoliters.

[0036] Based on the technical principle of this invention, the microdroplet generation method precisely controls the dynamic behavior of fluid by continuously generating three specific pressure stages on the time axis. These three stages are defined in sequence as the constant high pressure driving stage, the rapid pressure relief stage, and the oscillating negative pressure pull-back stage.

[0037] In the first timing phase, the constant high-pressure driving phase, the microcontroller sends an opening signal to the high-speed three-way solenoid microvalve. This phase begins at time T0 and ends at time T1, with the time span defined as the pulse width. During this period, the high-speed three-way solenoid microvalve remains energized, ensuring continuous conduction between its output terminal (terminal A) and the positive pressure input terminal (terminal B) connected to the pressure stabilizing chamber. Because the pressure stabilizing chamber is pre-filled with gas at a controlled pressure and gas source fluctuations are eliminated, the pressure in the fluid pipeline rapidly rises to the preset positive pressure peak at time T0 and maintains a constant pressure amplitude during the time interval from T0 to T1. This constant pressure characteristic is manifested in the gas pressure timing as a rectangular wave with a flat top. This constant positive pressure acts on the liquid surface in the reservoir, providing the initial kinetic energy required to overcome the surface tension at the gas-liquid interface at the nozzle, driving the liquid bend to break through the nozzle limitation and extend outward to form a liquid column. The extension length of the liquid column is positively correlated with the duration and pressure amplitude of this phase.

[0038] The second timing phase, starting at time T1, is the rapid pressure relief phase. When the preset pulse width is reached, the microcontroller cuts off the electrical signal sent to the high-speed three-way solenoid microvalve. The valve core assembly quickly resets under the action of the electromagnetic force and the return spring, cutting off the gas supply to the positive pressure input terminal (B terminal) and simultaneously connecting the output terminal (A terminal) and the waveform shaping terminal (C terminal). At this instant, the high-pressure gas accumulated in the pipeline is released to the external environment through the waveform shaping terminal and the one-way pressure relief valve at the front end. Logically, this phase is characterized by the pressure curve steeply decreasing from its peak to a baseline close to ambient pressure. The physical process of this phase aims to rapidly eliminate the positive pressure gradient driving the liquid to continue accelerating outward, suppressing excessive elongation of the liquid column under inertia, thereby limiting the main volume of the droplet.

[0039] The third timing stage is the oscillating negative pressure pull-back stage, which is a dynamic response directly induced by the pressure relief action. When the high-pressure gas in the pipeline is rapidly discharged through the two equivalent necks, waveform shaping end 213 and one-way pressure relief valve 310, the inertia of the gas mass block and the compressibility elasticity of the gas inside the pipeline form an underdamped oscillating system. Since the pipeline of the Helmholtz oscillation module 300 has a certain volumetric elasticity, excessive gas discharge will cause the pressure inside the pipeline to drop instantaneously below the ambient pressure (i.e., the downthrow phenomenon in overdamped or underdamped oscillation), thereby inducing aerodynamic resonance. This resonance generates a significant reverse negative pressure wave in the pipeline. This negative pressure wave is transmitted along the pipeline at the speed of sound to the nozzle tip, applying an instantaneous physical back suction force to the root of the forming liquid column. This back suction force interacts with the outward inertial force of the liquid column, causing the liquid column to undergo a necking effect at the nozzle outlet section, accelerating the breakage and separation process of the droplet neck. This negative pressure pull-back mechanism directly blocks the adhesion at the tail of the liquid column, preventing the formation of accompanying satellite droplets after the main droplet separates. The entire three-segment waveform cycle ends after the droplet completely detaches from the nozzle, and the system then returns to its initial equilibrium state, awaiting the arrival of the next trigger cycle.

[0040] See attached document Figure 2 The microdroplet generation system of the present invention uses a microcontroller to precisely control the on / off state of the solenoid valve, coordinates the airflow interaction between the pressure stabilizing gas source, the pressure relief passage and the oscillation cavity, and realizes the dynamic propagation and shaping of the gas pressure waveform in the fluid pipeline.

[0041] In the initial stage of the execution process, the system is in standby mode, the microcontroller outputs a low-level signal, and the high-speed three-way solenoid microvalve is in a power-off reset state. At this time, the first port (output terminal) and the third port (waveform shaping terminal) are connected, and the internal pressure of the pipeline remains balanced with the ambient pressure. When a jet trigger command is received, the microcontroller sends a high-level drive signal to the high-speed three-way solenoid microvalve, driving the valve core position to switch, closing the third port and connecting the first port and the second port (positive pressure input terminal). At this time, the constant high-pressure gas, buffered by the pressure stabilizing chamber, instantly rushes from the second port into the first port and is transmitted to the front end along the main gas pipeline. Because the pressure stabilizing chamber pre-stores gas with stable potential energy, the pressure in the gas path can establish a stable high-pressure platform within microseconds. This constant gas pressure directly acts on the gas-liquid interface in the nozzle module, pushing the liquid to overcome the capillary resistance at the nozzle and accelerate outward to form an initial liquid column.

[0042] When the duration of the high-level drive signal reaches the preset pulse width value, the microcontroller immediately cuts off the drive signal, and the system enters the pressure relief and waveform reshaping stage. The high-speed three-way solenoid microvalve is instantly de-energized and reset, the regulated gas source input at the second port is physically cut off, and the first port is reconnected to the third port. At this time, the high-pressure gas accumulated in the main gas pipeline has two release paths: on the one hand, the one-way pressure relief valve at the front end is opened by the pressure difference, directly discharging some of the residual high-pressure gas to the atmosphere, realizing a rapid and steep drop in pipeline pressure and eliminating the inertial force that pushes the liquid column to continue to extend; on the other hand, some of the return gas rushes into the third port through the first port.

[0043] When the high-pressure gas in the pipeline is instantaneously released through the first port and impacts the fluid loop at the third port, the pressure pulsation of the airflow at the neck of the cavity excites the Helmholtz oscillating chamber to generate aerodynamic resonance. This resonance phenomenon causes a negative pressure wave relative to the ambient air pressure to be instantaneously generated in the pipeline area connected to the third port. Since the first and third ports are in a conductive state at this time, the negative pressure wave can pass through the valve body in the reverse direction and propagate towards the front end along the main gas pipeline. When the negative pressure wave reaches the front one-way pressure relief valve, because the pressure in the pipeline drops below the ambient pressure, the one-way pressure relief valve automatically closes under the action of the reverse pressure difference, blocking the backflow of external air, thereby ensuring the lossless transmission of negative pressure wave energy in the pipeline.

[0044] Ultimately, the negative pressure wave propagates into the liquid cavity of the nozzle module, applying a sharp backward pull on the root of the liquid column forming at the nozzle exit. This pull counteracts the forward momentum of the liquid generated during the previous high-pressure pushing phase, causing the liquid column to rapidly contract and physically break at the nozzle exit section. This negative pressure pull mechanism, actively excited by the rear-end oscillating circuit, forces the fluid to separate at a predetermined position, eliminating the long tail phenomenon caused by liquid viscous stringing in traditional pneumatic dispensing, and preventing the formation of satellite droplets due to secondary aggregation of residual liquid after the main droplet breaks, thus ensuring the high consistency and morphological integrity of the microdroplet generation process.

[0045] See attached document Figure 3 In jet mode, the system is configured to perform a complete kinetic cycle from fluid extrusion to droplet separation. This mode relies in particular on the coordinated action of the one-way pressure relief valve located at the handheld end and the waveform generator at the rear end to ensure the fidelity and effectiveness of the pressure waveform during long-distance transmission.

[0046] When the system executes the injection command, the airflow path is initially in a positive pressure driven state. At this time, the constant high-pressure gas output from the rear pneumatic control module is transmitted to the Helmholtz oscillation module along the main air path pipeline. The main structure of the one-way pressure relief valve defines a through-flow central channel, which serves as the physical channel for waveform transmission, guiding the positive pressure airflow from upstream to the end nozzle module without obstruction. During this stage, the pipeline is under high pressure, and the airflow flows through the central channel of the one-way pressure relief valve at high speed. Utilizing the principles of fluid dynamics (or the Bernoulli effect), the high-speed airflow generates an adsorption force or normal thrust on the elastic sealing element of the one-way pressure relief valve, causing it to overcome the static pressure inside the pipe and fit tightly against the exhaust valve seat, thereby keeping the exhaust path closed. This airflow impact locking mechanism ensures that the driving energy does not leak and acts entirely on the gas-liquid interface inside the nozzle, pushing the liquid meniscus to overcome surface tension and extend outward to form a liquid column.

[0047] At the instant the injection pulse ends, i.e., when the downstream microvalve is de-energized and switches to the waveform shaping end, the pneumatic state within the pipeline undergoes a sharp reversal. At this moment, the one-way pressure relief valve immediately transforms from a transmission channel into a rapid venting assembly. Responding to the sudden disappearance of the upstream driving pressure, the airflow velocity through the central flow channel drops sharply, and the airflow holding force acting on the sealing element disappears. Simultaneously, the internal sealing element of the one-way pressure relief valve, propelled by the residual static pressure within the pipeline, rapidly disengages from the valve seat, opening a pressure relief path to the external environment. The residual high-pressure gas accumulated at the front-end handheld part and near the nozzle is rapidly and conveniently released into the atmosphere through this pressure relief path. This convenient pressure relief mechanism shortens the gas emission path length, causing the positive pressure acting on the liquid column to drop sharply within milliseconds, eliminating pressure hysteresis caused by the gas compression effect in long pipelines, thereby effectively preventing excessive elongation of the liquid column under inertia.

[0048] Subsequently, when the negative pressure wave generated inside the Helmholtz oscillating module is transmitted along the air path to the front end, the one-way pressure relief valve switches its operating state again to maintain the one-way sealing of the air path. As the pipeline becomes negatively pressured relative to the external environment, the external atmospheric pressure acts on the sealing element of the one-way pressure relief valve, forcing it to press tightly against the valve seat at the exhaust port, thus completely preventing backflow of external air into the air path. At this time, the central flow channel of the one-way pressure relief valve again acts as a lossless transmission channel, allowing the negative pressure wave from the rear end to pass through the valve body and directly act on the root of the liquid column at the nozzle. This mechanism ensures that the negative pressure energy does not attenuate due to leakage, thereby generating a sufficiently strong pull force at the neck of the liquid column, causing the droplet to break sharply at a predetermined time and position, achieving precise spraying without long tails or satellite droplets.

[0049] See attached document Figure 4The liquid loading mode of this invention refers to the process by which the system uses negative pressure to draw in external liquid through the nozzle orifice and fill the internal cavity of the nozzle body. In this mode, the one-way closing characteristic of the front-end one-way pressure relief valve plays a decisive role in sealing the air passage, ensuring the effective transmission of negative pressure suction and the precise loading of liquid.

[0050] When the system executes the liquid loading command, the back-end pneumatic control module switches to negative pressure suction mode. In this configuration, by activating the negative pressure generator connected to the air circuit or reversing the air pump, the air pressure inside the main air circuit pipeline is reduced to a negative pressure level lower than the external atmospheric pressure. This change in pressure state establishes a pressure gradient pointing towards the back end within the pipeline.

[0051] In response to a decrease in internal pipeline pressure, the one-way pressure relief valve located in the Helmholtz oscillation module automatically enters the reverse shut-off state. The valve core or sealing diaphragm of the one-way pressure relief valve is subjected to the pressure difference between the external atmospheric pressure and the negative pressure inside the pipeline, generating a clamping force pointing towards the valve seat. This clamping force forces the sealing element to fit tightly against the sealing interface inside the valve body, thereby physically cutting off the connection between the exhaust passage and the external environment.

[0052] This pressure differential-driven self-locking sealing mechanism effectively blocks the path of external air backflow into the main air duct through the pressure relief port. Because the exhaust path is completely blocked, the main air duct transforms into a closed negative pressure chamber with an opening only at the nozzle tip. Therefore, the negative pressure energy generated at the rear end can be faithfully transmitted along the duct to the internal cavity of the nozzle module without leakage loss.

[0053] At the nozzle tip, because the pressure inside the cavity is lower than the surface pressure of the external liquid, a pressure difference sufficient to overcome the liquid surface tension and flow resistance is formed at the nozzle orifice cross-section. This pressure difference drives the external liquid through the nozzle orifice, flows counter-currently along the micro-conical flow channel, and fills the liquid storage chamber of the nozzle body. Throughout the liquid filling process, the continuous sealing of the one-way pressure relief valve ensures that the pressure balance at the gas-liquid interface is entirely determined by the control source at the back end, avoiding problems such as poor liquid absorption, air bubble mixing, or inaccurate liquid volume control caused by gas leakage.

[0054] The microdroplet generation system of the present invention employs a time-domain-based flow control strategy, wherein the microcontroller 110 is configured to precisely modulate the time-domain characteristics, i.e., the pulse width, of the drive signal sent to the high-speed three-way solenoid microvalve 210. This pulse width is physically defined as the duration for which the high-speed three-way solenoid microvalve 210 remains in the second position (i.e., the input and output ends of the regulated gas source are in a conducting state).

[0055] In the dynamics of droplet formation, the pulse width directly determines the duration of the driving energy acting on the fluid interface. When the microcontroller 110 issues a driving command, pressurized gas enters the fluid pipeline and deforms the liquid meniscus. This process is an energy accumulation process, and the total aerodynamic energy input to the system is positively correlated with the pulse width. By adjusting this time parameter, the system can linearly or quasi-linearly change the volume of fluid discharged in a single injection cycle while keeping the input gas pressure amplitude constant.

[0056] To ensure the physical stability of droplet formation, this embodiment sets a minimum critical threshold for pulse width. Defined by hydrodynamics, this minimum pulse width is set to 1.5 milliseconds. When the set pulse width is below this critical value of 1.5 milliseconds, the aerodynamic energy transmitted to the nozzle tip is insufficient to overcome the surface tension barrier of the liquid at the micro-conical nozzle due to the excessively short airflow opening time. In this critical state, the liquid meniscus only undergoes reciprocating oscillations or a slight bulge followed by retraction, failing to complete necking and breakage to form independent droplets. Therefore, the control algorithm of the microcontroller 110 incorporates this lower limit constraint to prevent the execution of invalid injection commands.

[0057] Within an effective adjustment range greater than 1.5 milliseconds, the microcontroller 110 discretely or continuously adjusts the pulse width with millisecond-level resolution. As the pulse width increases, the duration of the constant high-pressure push phase lengthens, allowing more liquid to be pushed away from the nozzle before the rapid depressurization and negative pressure pull-back actions occur. This time-window-based volume cutoff mechanism enables the system to precisely control the length of the liquid column before it breaks.

[0058] By combining pulse width modulation with pressure regulation of the 220 pressure chamber, the system can achieve continuous, precise, and on-demand setting of droplet volume across a wide range from 400 picoliters to 20 nanoliters, meeting the quantitative requirements for micro-fluid distribution under different operating conditions. Furthermore, this dual-variable synergistic regulation mechanism also endows the system with adaptability to different fluid viscosities. For viscosity ranges within... to For fluids with varying viscosity (centipoise), the system can compensate for the flow resistance loss caused by high viscosity by increasing the input air pressure of the pressure stabilizing chamber 220, and at the same time adjust the pulse width accordingly, thereby maintaining the consistency of droplet volume in media with different viscosities without the need to replace the nozzle module.

[0059] Furthermore, a bivariate collaborative regulation mechanism is provided to achieve precise definition of droplet volume over a wide dynamic range. Specifically, the bivariate variables refer to the gas pressure amplitude within the plenum and the opening pulse width of the high-speed three-way solenoid microvalve. Through the cooperation of a microcontroller and precision pressure regulating components, the system achieves continuous volume regulation within a range of 400 picoliters to 20 nanoliters.

[0060] In the volume regulation mechanism, the gas pressure amplitude determines the instantaneous flow velocity and kinetic energy density of the fluid at the nozzle. A microcontroller or external pressure regulator is configured to set the base pressure input to the plenum. When generating tiny droplets close to the lower limit of the range (e.g., 400 picoliters to 1 nanoliter), the system is configured to employ a combination of low pressure and short pulse width. Under this condition, the lower driving pressure causes the fluid to be expelled at a lower Weber number, and the short pulse width (approximately 1.5 milliseconds) near the critical threshold limits the total amount of fluid ejected.

[0061] In particular, for extremely small droplets of 400 picoliters, the surface tension of the fluid plays a significant role, and conventional gravity or inertia is insufficient to cause them to fall off naturally. In this case, the oscillating negative pressure pull-back mechanism of this system plays a key role. By actively applying negative pressure waves, it overcomes the surface tension and forces the tiny droplets to break within an extremely short necking length, thereby achieving stable control of this extremely small volume.

[0062] When generating larger droplets near the upper limit of the range (e.g., 1 nanoliter to 20 nanoliters), the system is configured to increase the input pressure amplitude of the plenum and correspondingly lengthen the pulse width. The increased pressure provides higher fluid acceleration, resulting in increased flow rate through the nozzle per unit time; the extended pulse width allows more fluid to flow out over time. By positively superimposing the pressure amplitude and pulse width, the system can linearly or non-linearly amplify the volume of a single injection.

[0063] The adjustable range is also achieved thanks to the micro-conical structure of the nozzle module and its adaptation to different inner diameter specifications. For specific volume requirements, by selecting a nozzle orifice diameter with specific flow resistance characteristics and adjusting the aforementioned pressure and time parameter matrix, the system can cover the entire volume range from 400 picoliters to 20 nanoliters while ensuring droplet sphericity and flight trajectory stability. The microcontroller internally stores pre-calibrated parameter lookup tables or algorithm models to automatically match the optimal combination of pulse pressure and pulse width based on the target volume.

Claims

1. A method for generating microdroplets based on a three-segment gas pressure waveform, characterized in that, Includes the following steps: The microcontroller sends timing control commands to drive the pneumatic components to move, which are then executed sequentially in the fluid pipeline: During the constant high pressure driving stage: the microcontroller sends an opening signal to the high-speed three-way solenoid microvalve, driving the valve core to switch to the state of connecting the positive pressure input end and the output end. The constant high pressure gas, which is buffered by the pressure stabilizing chamber, is transmitted along the main gas pipeline, driving the liquid bend surface to extend at the nozzle to form a liquid column. Rapid pressure relief phase: When the duration of the opening signal reaches the preset pulse width, the opening signal is cut off, the high-speed three-way solenoid microvalve is reset and the output terminal is connected to the waveform shaping terminal, and the high-pressure gas accumulated in the pipeline is released to the external environment through the waveform shaping terminal and the one-way pressure relief valve; During the oscillating negative pressure pull-back stage: the gas path switching at the moment of reset of the high-speed three-way electromagnetic microvalve causes the fluid system composed of the main gas path pipeline, the high-speed three-way electromagnetic microvalve, and the one-way pressure relief valve to form a Helmholtz oscillating cavity structure. The rapid release of gas in the pipeline induces aerodynamic resonance and generates a reverse negative pressure wave in the main gas path pipeline. The reverse negative pressure wave is transmitted to the nozzle and applies a physical back suction force to the root of the liquid column, causing the neck of the liquid column to break and separate, forming micro-droplets.

2. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 1, characterized in that, The high-speed three-way electromagnetic micro-valve is provided with a first port, a second port and a third port; The first port is defined as the output terminal and connected to the main gas pipeline; the second port is defined as the positive pressure input terminal and connected to the pressure stabilizing chamber; and the third port is defined as the waveform shaping terminal and connected to the negative pressure source or atmospheric environment. During the constant high pressure driving phase, the high-speed three-way electromagnetic microvalve is in a second position where the first port and the second port are connected and the first port and the third port are disconnected. During the rapid depressurization phase and the oscillating negative pressure pull-back phase, the high-speed three-way electromagnetic micro-valve is in a first position where the first port and the third port are connected and the first port and the second port are disconnected.

3. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 2, characterized in that, The pressure stabilizing chamber is configured as a gas buffer container with a predetermined volume, with its input end connected to a high-pressure gas source and its output end connected to the second port. During the constant high pressure driving phase, the pressure stabilizing chamber inputs high-pressure gas with a constant amplitude to the second port. The pressure in the fluid pipeline rises to a preset positive pressure peak at the moment the opening signal is triggered, and maintains a constant pressure amplitude during the pulse width duration.

4. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 2, characterized in that, The Helmholtz oscillation chamber structure is not an independent component, but is composed of the main air passage as a volume chamber, and the third port of the high-speed three-way solenoid microvalve and the pressure relief port of the one-way pressure relief valve as oscillation neck ports. During the oscillating negative pressure pull-back phase, the high-pressure gas in the main gas pipeline is released bidirectionally through the third port and the one-way pressure relief valve. The airflow inertia and pipeline volume effect interact to generate underdamped oscillations, thereby exciting the reverse negative pressure wave inside the main gas pipeline.

5. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 1, characterized in that, The one-way pressure relief valve is installed on the main gas pipeline and has a through central flow channel and an elastic sealing element. During the constant high pressure driving stage, the high-speed airflow flows through the central flow channel, and the elastic sealing element overcomes the static pressure inside the pipe and adheres to the exhaust valve seat under the action of the airflow impact and adsorption force, thus sealing the exhaust path. During the rapid depressurization phase, the airflow velocity through the central flow channel decreases, and the elastic sealing element is disengaged from the exhaust valve seat under the push of the residual static pressure in the pipeline, opening a depressurization path to the external environment.

6. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 5, characterized in that, The microdroplet generation method also includes a liquid loading mode, in which the system switches to a negative pressure suction state, and a pressure gradient pointing towards the rear end is formed inside the main gas path pipe. The elastic sealing element of the one-way pressure relief valve generates a clamping force pointing towards the exhaust valve seat under the pressure difference between the external atmospheric pressure and the negative pressure inside the pipeline, sealing the exhaust channel from the external environment. Under the negative pressure suction force transmitted to the nozzle orifice, the nozzle module draws external liquid into the internal cavity of the nozzle body.

7. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 1, characterized in that, The microcontroller is set with a minimum critical threshold for the pulse width, which is set to 1.5 milliseconds; When the set pulse width is less than 1.5 milliseconds, the microcontroller is prohibited from sending the enable signal.

8. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 1, characterized in that, The microcontroller is equipped with a dual-variable collaborative adjustment mechanism based on pressure amplitude and pulse width; When generating tiny droplets close to the lower limit of the range, a combination of low gas pressure and short pulse width is used, and the reverse negative pressure wave generated during the oscillating negative pressure pull-back stage is directly applied to the root of the liquid column. When generating larger droplets close to the upper limit of the range, a combination of increasing the input pressure amplitude of the stabilizing chamber and extending the pulse width is used.

9. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 1, characterized in that, The nozzle has a single-hole micro-conical structure with a rear inner diameter larger than the front inner diameter; the method further includes configuring a nozzle orifice diameter with predetermined flow resistance characteristics and setting a pulse width that matches the nozzle orifice diameter.

10. The microdroplet generation method based on a three-segment gas pressure waveform according to claim 8, characterized in that, The dual-variable collaborative regulation mechanism includes compensation logic for different fluid viscosities; for fluids with viscosity ranging from 1 mPa·s to 1000 mPa·s, it performs operations to increase the input air pressure and adjust the pulse width so that the volume of the droplets ejected through the nozzle is maintained within a preset range.

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